The de minimus exception is probably the most appropriate exception in your case, but it requires significant accounting for the prime contractor, who must account for all of the excepted specialty metals in the end item weapons system to ensure that the total remains below the 2 percent level.
"(1) Notwithstanding subsection (a), the Secretary of Defense or the Secretary of a military department may accept delivery of an item containing specialty metals that were not melted in the United States if the total amount of noncompliant specialty metals in the item does not exceed 2 percent of the total weight of specialty metals in the item.
(2) This subsection does not apply to high performance magnets."
The law also defines "end item" as "the final production product when assembled or completed, and ready for issue, delivery, or deployment."
The other alternatives you mentioned are not appropriate to your circumstances.
- The DNAD was extensively used by the Services prior to 2009, but since then, the DNAD exception applies to the specialty metal itself, not to the manufactured part. This has become very difficult to prove.
- The national interest waiver is designed for errors discovered after the fact and may be approved for certain blocks of runs until the design could be changed. The national interest waiver has a very high standard. Only USD(AT&L) can approve such a waiver. It requires congressional notification, and it requires an investigation to determine if the error was knowing and willful on the part of the contractor.